﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _实体值测试
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Enumerable.Range(1, 100).Where(x => (x & 1) == 0).Sum());

            int? a = null;
            string b = a == null ? "0" : a.ToString();
            string c = a?.ToString();
            string d = "";
            string e = d?.ToLower();

            Console.WriteLine(b);
            Console.WriteLine(c);

            Console.ReadKey();
        }
    }

}
